The CPU usage isn't that bad compared to some of the other things we did in the demo - with some help from interrupts it could be done with maybe 20% of CPU. Th

The CPU usage isn't that bad compared to some of the other things we did in the demo - with some help from interrupts it could be done with maybe 20% of CPU. There is also a much easier ~500 colour variant which doesn't take any CPU time at all once set up. I think the real reason it wasn't discovered earlier is that most CGA PCs were not connected to composite monitors or TVs (people who could afford the big expensive IBM machine could generally afford a dedicated digital monitor as well). A few games used 160x200x16 composite but even those generally had modes for RGBI monitors as well (which wouldn't work so well with the 500/1K colour modes, though I guess there are the dithering characters 0xb0 and 0xb1 which might have worked). These +HRES modes also suffer from CGA snow, which might have been a deal-breaker.